Abstract:
The chemical ecology for key insect pests in South Africa's commercial Pinus and Eucalyptus
plantations are explored in this thesis. The main aim was to discover and
characterize semiochemical compounds that explain certain behaviours of the insects
involved, and that could potentially be exploited in future for the manipulation of the
insects' behaviour. Such formulations are sought after because they can be applied in
environmentally friendly pest management techniques. Semiochemical interactions were
studied in four di erent biological systems. These included the sex pheromone communication
system for the Cossid moth, Coryphodema tristis; allelochemical interactions
between the Eucalyptus weevil Gonipterus spp. and their Eucalyptus host; allelochemical
interactions between Sirex noctilio's, symbiotic fungus, Amylostereum areolatum and
its biological control agent Ibalia leucospoides; and allelochemical interactions between
the egg clutches of Thaumastocoris peregrinus and its biological control agent Cleurocoides
noackae. Semiochemical compounds were found and identi ed through analysis
techniques that included gas chromatography coupled to electroantennography (GCEAD)
and gas chromatography coupled to mass spectrometry (GC-MS). Some of these
semiochemical interactions were complex involving combinations of di erent chemical
cues, such as the host recognition cues identi ed for Gonipterus species and potential
cues between T. peregrinus females and their egg clutches. Other speci c interactions
were found to be simpler and relied on a few speci c chemicals. These included the
sex pheromone communication between C. tristis adults and the interaction occurring
between female I. leucospoides wasps and the mutualistic fungus of their prey, namely
A. areolatum. Biological activity was investigated only for compounds with con rmed
identity and included the sex pheromones of C. tristis and some of the chemicals identi
ed from the egg clusters of T. peregrinus. These tests were conducted in laboratory
and eld conditions. Biological activity was proven for the identi ed sex pheromone of
C. tristis during eld trials conducted in 2011 and 2013. One of the chapters was published
and another submitted for publication in a peer reviewed journal. Two provisional
patents were also registered from this work.
